In recent years, requirement for fuel oil standards becomes increasingly stricter due to the consideration of environmental protection worldwide. For instance in China, “Controlling Criterion of Hazardous impurities for Car Gasoline” has been drown up by National Quality Monitoring Bureau in 1999. According to the requirement of this Criterion, the sulfur content of gasoline as a finished product must be less than 800 ppm. In fact, more than 90% of sulfur in finished gasoline comes from FCC gasoline. On the other hand, the tendency that catalytic cracking feedstock grows heavier is becoming increasingly acute, and the proportion of middle-east crude oils refined by refineries in China is increasingly high, which have higher sulfur content. Therefore, there is a desire to develop a cracking catalyst with higher cracking activity and higher sulfur reduction activity.
U.S. Pat. No. 6,036,847 and its family patent EP 0,798,362 A2 disclose a process for fluidized catalytic cracking a hydrocarbon feedstock, wherein said hydrocarbon feedstock is cracked in a cracking zone in absence of added hydrogen, and all particles including catalyst particles are repeatedly circulated between a hydrocarbon cracking zone and a catalyst regeneration zone, wherein said all particles contain additional particles having less activity for catalyzing the cracking of hydrocarbon oils compared to said catalyst particles, said activity being on a fresh particle basis. The additional particles consist essentially of titania and inorganic oxide other than titania. Said inorganic oxide other than titania contains Lewis acid selected from the group consisting of elements and compounds of nickel, copper, zinc, silver, cadmium, indium, tin, mercury, thallium, lead, bismuth, boron, aluminum (other than alumina) and germanium supported on alumina. The sulfur content of FCC gasoline in cracked products is decreased by using this type of additive containing titanium oxide.
U.S. Pat. No. 5,376,608 discloses a cracking catalyst composition having a function of desulfurization, which comprises (a) a zeolite/molecular sieve dispersed in an inorganic oxide matrix; (b) a Lewis acid-containing alumina component which comprise from 1 to 50% by weight of Lewis acid selected from the group consisting of elements and compounds of nickel, copper, zinc, silver, cadmium, indium, tin, mercury, thallium, lead, bismuth, boron, aluminum (other than alumina) and germanium supported on alumina.
WO 99/49001A1 discloses a composition for reducing the sulfur content of hydrocarbon components, wherein said composition contains a hydrotalcite material which has been impregnated with a Lewis acid and optionally a FCC catalyst. Said Lewis acid comprises transition metal elements, especially zinc, copper, nickel, cobalt, iron or manganese, and their compounds.
WO 01/21733A1 discloses a catalytic cracking process for cracking a hydrocarbon feedstock containing organo-sulfur compounds in the presence of hot regenerated cracking catalyst. Said catalyst contains a product sulfur reduction component containing a metal component in an oxidation state greater than zero. Said metal component includes compounds or complexes of metal elements selected from the group consisting of Period 3, Groups VB, VIIB, VIII, IIB and IVA of the periodic table, such as metal compounds or complexes of vanadium, zinc, iron, cobalt, manganese and gallium. Said product sulfur reduction component comprises a molecular sieve of which the porous structure contains aforementioned metal component, also comprises aforementioned metal component dispersed anywhere on the catalyst carrier structure, e.g. a porous oxide carrier.
WO 01/21732A1 discloses a process for reducing the sulfur content of a cracked petroleum fraction, comprising catalytically cracking a petroleum feed fraction at elevated temperature in the presence of cracking catalyst and a product sulfur reduction additive to obtain liquid cracking products of reduced sulfur content, wherein said product sulfur reduction additive comprises a non-molecular sieve carrier containing vanadium; said non-molecular sieve carrier may be an organic or inorganic carrier; preferred the carrier is amorphous or paracrystal inorganic oxides, such as alumina, silica, clay or their mixture.
CN 1281887A discloses a process for reducing the sulfur content of catalytically cracked petroleum fractions, comprising catalytically cracking a petroleum feed fraction at elevated temperature in the presence of a product sulfur. reduction catalyst to produce liquid cracked products of reduced sulfur content. The product sulfur reduction catalyst contains a porous molecular sieve having a metal component which is within the interior pore structure. Said porous molecular sieve may be a large pore size zeolite, i. e. the zeolite having a pore structure with a ring pore opening of at least 0.7 nm such as, Y-zeolite, rare-earth Y-zeolite (REY), ultra-stable Y-zeolite (USY), L-zeolite, beta-zeolite, mordenite, ZSM-18 zeolite. Said molecular sieves may also be a intermediate pore size zeolite, i. e. the zeolite having a pore structure with a ring pore opening of larger than 0.56 nm but smaller than 0.7 nm such as Pentasil zeolite, ZSM-5 zeolite, ZSM-22, ZSM-23 zeolite, ZSM-35 zeolite, ZSM-50 zeolite, ZSM-57 zeolite, MCM-22 zeolite, MCM-49 zeolite, MCM-56 zeolite. Said molecular sieves may further be non-zeolite molecular sieves such as silicates of varying silica-alumina ratios (e.g. metallosilicates, titanosilicates), metalloaluminates (e.g. germaniumaluminates), metallophosphates, aluminophosphates, metalloaluminophosphates, metal integrated silicoaluminophosphates (MeAPSO and ELAPSO), silicoaluminophosphates (SAPO), gallogermanates and combinations of these.
CN 1261618A discloses a process for reducing the sulfur content of a catalytically cracked petroleum fraction, comprising catalytically cracking a petroleum feed fraction containing organo-sulfur compounds at elevated temperature in the presence of a cracking catalyst and a product sulfur reduction catalyst to produce liquid cracked products of reduced sulfur content. Said product sulfur reduction catalyst contains a porous molecular sieve containing a first metal component and a second metal component. Said first metal component is within the interior pore structure of the molecular sieve and exists in an oxidation state greater than zero. The second metal component comprises at least a rare-earth element and is within the interior pore structure of the molecular sieve. Said first metal component is a metal selected from the group consisting of elements of Period 4 and Groups IIB, VB, IIIA and VIII of the periodic table, especially vanadium, zinc, iron, gallium.
Since aforesaid catalysts are subjected to drying, calcining and/or hydrothermal treating without reduction process during the preparation of them, the metal component contained in aforesaid catalysts exists all in respective maximum oxidation states.
CN 1382199A discloses an adsorbent composition, consisting of a bimetal promoter and a granular carrier, said bimetal promoter exists essentially in a reduction state in an amount enough to remove sulfur from cracked gasoline under desulfurization conditions. Said bimetal promoter is any two or more selected from the group consisting of cobalt, nickel, iron, manganese, copper, zinc, molybdenum, tungsten, silver, tin, antimony and vanadium. Said carrier consists of zinc oxide in combination with any suitable inorganic and organic carrier. Said inorganic carrier includes silica, silica gel, alumina, clay, aluminum silicate, silica-alumina, titanium oxide, zirconia, zinc aluminate, zinc titanate, zinc silicate, calcium aluminate, calcium silicate, magnesium silicate, magnesium aluminate, magnesium titanate, synthetic zeolites and/or natural zeolites. The composition is used as an adsorbent for removing sulfur from cracked gasoline and diesel fuel, not as a cracking catalyst.
CA2444461 discloses an equilibrium cracking catalyst and a method for reducing sulfur content of gasoline fraction during the process of catalytically cracking. Said equilibrium cracking catalyst comprises at least one Y-type zeolite and Lewis acid addictive, wherein said lewis acid is a metal selected from the group consisting of Ni, Cu, Zn, Ag, Cd, In, Sn, Hg, Tl, Pb, Bi, B, Al, Mg, Mn, Ga or the combination thereof, and said metal is in zero valence state or is an oxide. The Lewis acid addictive is obtained by drying the alumina impregnated with the Lewis acid at mild temperature(100 to 150° C.), and calcining at 200 to 850° C. to remove the anionic portions of the Lewis acid salt. Although it is mentioned in the application that the metal can be in zero valence state, it is not suggested how to obtain a catalyst containing metals in zero valence state from the process.
An object of the present invention is to provide a novel molecular sieve-containing catalyst for cracking hydrocarbons, having higher cracking activity and higher sulfur reduction activity.
The inventor of the present invention has discovered that, if a metal component is introduced into a cracking catalyst in reduction state, not only the sulfur reduction activity of the cracking catalyst can be increased, but also, unexpectedly, the cracking activity of the cracking catalyst can be increased significantly.
The catalyst according to the present invention comprises molecular sieve, refractory inorganic oxide, clay and a metal component. The amount of the molecular sieve is from 1 to 90% by weight, the refractory inorganic oxide is from 2-80% by weight, the clay is from 2 to 80% by weight, and the metal component is from 0.1 to 30% by weight calculated as the oxide of said metal having its maximum valence state, based on the total amount of the catalyst. Said metal component exists essentially in a reduction state and is one or more metals selected from the group consisting of metals of Group IIIA (other than aluminium), and metals of Groups IVA, VA, IB, IIB, VB, VIB, VIIB, and non-noble metals of Group VIII of the periodic table.
The process for preparing the catalyst according to the present invention comprises contacting the composition comprising metal-containing component compound, molecular sieve, refractory inorganic oxide and clay with a reducing gas-containing atmosphere at enough temperature for enough time so that the metal component has an average valence state less than its maximum oxidation state. Said metal component is one or more metals selected from the group consisting of metals of Group IIIA (other than aluminum), and metals of Groups IVA, VA, IB, IIB, VB, VIB and VIIB, and non-noble metals of Group VIII of the periodic table. The amount of each component is such that the final catalyst comprises, based on the total amount of the catalyst, from 1 to 90% by weight of the molecular sieve, from 2 to 80% by weight of the refractory inorganic oxide, from 2 to 80% by weight of the clay, and from 0.1 to 30% by weight of the metal component, calculated as the oxide of said metal having its maximum valence state.
Compared with the catalyst of the prior art, the catalyst according to the present invention has higher sulfur reduction activity, and further, unexpectedly, higher cracking activity. For example, by using the catalyst of the present invention, which contains 30 wt % of MOY-zeolite, 34 wt % of alumina, 35 wt % of kaolin, 1 wt % of cobalt, calculated as Co2O3, in which cobalt has +1.5 of an average valence state (thereby the ratio value of the average valence state to maximum valence state of cobalt is 0.5), (after deactivated by steam-aging at 800° C. for 8 hours, then reduced), the catalytically cracking of the vacuum gas oil with a distillation range of 329-550° C. and a sulfur content of 2.0% by weight was carried out under conditions of a reaction temperature of 500° C., a WHSV of 16 hr−1, a weight ratio of catalyst to oil of 4.0, as a result, the conversion was 78.6% by weight, the sulfur content of gasoline product was only 416.7 mg/l. However, when a cracking catalyst having the same content of zeolite but no cobalt and a catalyst having all the same contents of each component but cobalt only in its maximum valence state(+3 valence) were used to carry out the catalytic cracking reaction of the same feedstock oil at the same conditions, only 68.9 wt % and 75.1 wt % of conversions were obtained respectively, and the sulfur contents of gasoline products were up to 758.3 mg/l and 670.6 mg/l, respectively.